In many electrophotographic printing systems, such as electrophotographic printers or electrophotographic copiers, a photoconductor drum is used for generating a latent electrostatic image onto which toner is subsequently developed. During the printing process, the surface of the photoconductor drum contacts print media and other components of the electrophotographic printing system, such as a transfer roller, during rotation. The contact from the printing process results in wear on the surface of the photoconductor drum. The resulting wear limits the useful life of the photoconductor drum.
Typically, in electrophotographic printing systems, the print media passes between the rotating photoconductor drum and the transfer roller or a backup roller. Generally, in electrophotographic printing systems, after the trailing edge of the last sheet of print media in the print job has passed out of the nip region between the photoconductor drum and the transfer roller or backup roller, the photoconductor drum undergoes several post print media rotations. These post print media rotations contribute to the wear on the photoconductor drum.
For the case in which printing is done primarily on single page jobs, the resulting rate of wear is much greater than for multi-page jobs because the number of post rotations per page is considerably higher than for multiple page jobs. Consider, for example, an electrophotographic printer. In electrophotographic printers, the photoconductor drum is typically gear driven as part of a gear train which drives rollers used in all parts of the print media path. The gear train must continue to rotate after the print media has moved beyond the photoconductor drum to move the print media through the remainder of the steps in the electrophotographic printing process and to the output tray. Therefore, as the print media moves toward the output tray after passing the photoconductor drum, the photoconductor drum continues to rotate. These additional rotations cause unnecessary wear on the surface of the photoconductor drum, thereby needlessly shortening the useful life of the photoconductor drum.
For electrophotographic printers with print media paths which are long relative to the dimension of the print media parallel to the direction of movement of print media through the print media path, the reduction in the useful life of the photoconductor drum is especially severe. The reduction in useful life of the photoconductor drum is especially severe for the case in which the predominant use of the printer is for the printing of single page jobs, because many more rotations of the photoconductor drum occur than would have occurred if the same number of pages had been printed using multiple page print jobs. In some electrophotographic printers having relatively long print media paths, printing single page jobs requires three times as many rotations of the photoconductor drum as are required for transfer of the developed image onto the print media.
In some electrophotographic printers for which the print media path is not long relative to the dimension of the print media parallel to the direction of movement of print media through the print media path, the reduction in the useful life of the photoconductor drum can still be substantial. In some electrophotographic printers of this type, the control of the gear train which rotates the photoconductor drum is done with the default assumption that the print media which moves through the print media path is always the longest type of print media which the printer can handle. By designing the printer so that the printer performs as if all print media is of the longest type, the necessity of detecting the end of the page is eliminated, thereby reducing the cost of the printer. In these types of printers, even though the print media path of the printer is relatively short, single page jobs of letter size print media can still result in significant amounts of unnecessary wear. The unnecessary wear results from the incremental number of rotations of the photoconductor drum required from the default treatment of the print media as the longest possible type of print media.
Electrophotographic printers using a clutch to disconnect the photoconductor drum from the drive train of the electrophotographic printer have been disclosed in the prior art. In the disclosed implementations, the means used to disconnect the drive train of the electrophotographic printer from the photoconductor drum is part of the drive train of the electrophotographic printer. However, designing the means to disconnect the photoconductor drum from the drive train as part of the drive train places a limitation upon the ability to retrofit this capability into electrophotographic printers in the possession of customers. For some electrophotographic printers there may be a desire to implement the capability to reduce wear upon the photoconductor drum in electrophotographic printers already in the possession of customers. By including the means to disconnect the drive train within the drive train, implementing this capability would, in many cases, be prohibitively expensive. A need exists for an apparatus to permit the disconnecting of the photoconductor drum from the printer drive train that can be inexpensively retrofitted into field printers.